1. Field of the Invention
This invention relates to a hydraulic brake pressure control device for vehicles and, more particularly, to an improved control device for preventing the inboard rear wheel of the vehicle from locking upon brake application during the turning of the vehicle.
2. Description of the Prior Art
Devices for controlling the hydraulic braking pressure to the brake cylinder of an inboard wheel of a turning vehicle to prevent locking upon application of the brakes are known in the art. Typical of such apparatus is that disclosed in U.S. Pat. No. 3,890,014 to Hayes. These devices are required to compensate for the shift in load-bearing to the outboard wheel during a turn and the resultant decrease in the braking force required to lock the inboard wheel. That is, when the vehicle turns, the load upon the inner wheel with respect to the turning direction is made smaller while the load upon the outer wheel is made larger due to the laterally acting centrifugal force. When the brake is applied in such a condition, the inner wheel would be subject to be locked without hydraulic brake pressure control. The locking of the inner wheel may cause over-steering of the vehicle wherein a slight operation of the steering wheel causes a disproportionately large turning of the vehicle. Such vehicle response can be objectionable, as the safety of the driver of the vehicle may be compromised.
The overall objects of this invention are substantially the same as those of U.S. Pat. No. 3,890,014. That is, according to the invention which is an improvement over devices such as shown in U.S. Pat. No. 3,890,014, the brake force of the right and left wheels may be controlled to prevent locking the inboard wheel of the vehicle upon application of the brakes during a turn.
One of the significant drawbacks to the brake pressure controllers of the type disclosed in Hayes is that minor variations in the spring constants and/or manufacturing tolerances of the valve housing will result in different setpoints for the two proportioning valves. Such differences can result in a tendency for one wheel to "lock" before the other during straight-ahead operation as well as to cause different handling characteristics during braking on a curve, depending on whether a right or left hand turn is being made.
Another significant drawback to conventional hydraulic braking pressure controllers used to compensate for lateral motion is that the springs used to establish the setpoints at which the braking pressure for a particular wheel cylinder will be reduced relative to the master cylinder pressure are positioned inside the pressure boundary as in Hayes or are located as to require complete disassembly of the valve components for gaining access thereto. That is, with present controllers, biasing adjustments to the setpoints can be made only after dismantling the proportioning valve assemblies and then re-assembling the devices using springs with different K factors or pre-loads. The time for such disassembly/assembly coupled with the care needed to properly seal a high pressure apparatus make adjustments to the valve setpoints prohibitively expensive if the present improvement is not utilized.
The present invention, to be disclosed in greater detail in the portion of the specification that follows, not only automatically equalizes the exerting force of the springs in both valves, and thereby the setpoints, but also permits manual biasing adjustments to be made in the spring force quickly and easily without disturbing high pressure seals. The present invention ensures that any such increase or decrease in reduced pressure setpoints is the same for each of the two valves, thus providing for uniform vehicle response and handling during braking regardless of whether a right or left hand curve is being negotiated.
Another problem with conventional rear wheel brake pressure proportioning devices that are responsive to lateral movement involves unwanted changes in the overall front-to-rear proportionment during braking while turning. Present devices do not ensure that the magnitude of increased spring force (increased setpoint) on the valve controlling the outboard wheel has the same magnitude as the decrease of the spring force (lowered setpoint) on the valve controlling hydraulic braking pressure to the inboard wheel. A balancing of these magnitudes is often desirable in order that the degree of proportioning for the rear wheels taken as a whole in respect to the rear-to-front weight shift during braking will remain fairly constant. The present invention is also intended to solve this problem by providing improvements to existing apparatus.
Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.